CN1196866C

CN1196866C - Hydraulic seal for rotary pumps

Info

Publication number: CN1196866C
Application number: CNB008108498A
Authority: CN
Inventors: L·卡扎特克文; L·维瑞拉
Original assignee: Impsa International Inc
Current assignee: State Bureau Of Science And Technology
Priority date: 1999-07-26
Filing date: 2000-06-23
Publication date: 2005-04-13
Anticipated expiration: 2020-06-23
Also published as: CN1364213A; ATE307964T1; WO2001007760A1; DE60023523D1; DE60023523T2; EP1212516B1; EP1212516A4; US6247892B1; AU5634600A; AR023919A1; EP1212516A1; ES2252018T3

Abstract

A rotary blood pump comprising at least one rotor (1), a housing (3) and at least one conduit (16) in the rotor for conducting a by-passed portion of the blood into a clearance (9) between the rotor and the housing, the portion of blood consisting mostly of plasma without red blood cells, thus preserving the solid particles and red cells from damage.

Description

Hydraulic seal for rotary pump

Background of the invention

Field of the invention

The present invention relates to rotary pumps, and more particularly to axial rotary pumps with hydrodynamic bearings which propel fluid through at least one stage with minimal friction and with minimal or no shear forces imparted to the fluid, and more particularly to a hydraulic bearing and a continuous axial rotary pump for pumping fluids having particles or components which must be protected, for example, for use in blood circulation assistance equipment, or within an inner vascular circuit, or within an outer vascular circuit, from damage or destruction of red blood cells and platelets, and from thrombosis or thrombosis.

Although the present description refers to a blood pump as a specific reference, it should be clear that the pump can be used in any other field where it is necessary to transfer or transport any fluid from one place to another, both in a closed circulation system and in any open circuit or channel, such fluid preferably being a fluid whose composition is to be protected.

Description of the prior art

One type of axial flow rotary pump includes a generally cylindrical housing and/or stators having one or more motors mounted therein that drive fluid through the pump. Increasing the fluid pressure of the liquid by providing energy to the liquid may drive the liquid to transfer the liquid from the inlet of the pump to the outlet of the pump. However, this energy can produce several unwanted side effects. How to eliminate these side effects without compromising pumping efficiency has been the goal of much research and development in the field of pumps, particularly where handling sensitive fluids is involved, such as explosive fluids, blood, etc.

The shape, size, assembly and relative position of the various components and the fixed and movable surfaces of the pump are all aspects and parameters that need to be defined when referring to the pump. The ultimate goal of this design is to maximize the efficiency of the pump and minimize or eliminate side effects from the energy transferred to the fluid during the propelling of the fluid. In particular in the case of blood pumps, the aim to be achieved is to provide a pump with maximum efficiency, without the side effects of damaging the blood and/or causing coagulation of the blood during operation. Another important objective is to minimize the size of the pump.

Side effects caused by the energy transferred during rotation of the pump include secondary or side flows generated at the surfaces of the fixed and movable parts of the pump, turbulence, cavitation, and separation of the liquid flow.

The characteristics of a continuous flow of liquid through a rotary pump with vanes can be determined mathematically using Euler's equations. According to the Euler equation, the pressure applied by the rotor can be proportional to the increase in the tangential component of the velocity. The euler equation can be analyzed by the so-called velocity triangle shown in figure 1 of the commonly known scheme US 6247892. The vector represents the average velocity over the flow surface, and the letters used in fig. 1 are labeled:

angular velocity of omega

Radius R

R rotation speed u- ω

C absolute velocity

W relative velocity

C_uTangential component of absolute velocity

Reference numeral 1 is an inlet of the pump

Reference 2 is the outlet of the pump

The euler equation used on a typical rotary pump is:

{(R . C_{u})}_{2} - {(R . C_{u})}_{1} = \frac{g . H}{η . ω}

wherein,

h is water head

g is the acceleration of gravity

Eta is efficiency

If C is present_u10, then

C_{u 2} = \frac{g . H}{R}

This is why conventional pump constructions have stator vanes at the outlet of the pump, and therefore attempt to minimize the tangential component of velocity and convert this kinetic energy into pressure energy.

Despite the various efforts made in eliminating or at least reducing the above mentioned side effects, for example by reducing or eliminating the above mentioned tangential component, no solution has been found so far. When smaller reynolds numbers are involved, i.e. when one is operating a smaller pump and/or viscous liquid, the stator vanes at the pump outlet cannot effectively reduce the tangential component of velocity and convert kinetic energy into pressure energy, regardless of the shape or number of vanes. This therefore creates flow separation and side flow on the stator vanes which can cause hemolyses and blood clotting.

One type of axial flow rotary pump includes a generally cylindrical housing and/or stators having one or more motors mounted therein that drive fluid through the pump. Increasing the fluid pressure of the liquid by providing kinetic energy to the liquid may drive the liquid to transfer the liquid from the inlet of the pump to the outlet of the pump. However, the kinetic energy creates several unwanted side effects when propelling the fluid. How to eliminate these side effects without compromising the pumping efficiency of the pump has been the target of much research and development in the field of pumps, particularly where handling sensitive fluids is involved, such as explosive fluids, blood, etc.

Referring to blood pumps, rotary pumps for pumping blood, particularly those implanted in the human body, are known as circulatory aids, and can cause serious damage to the blood, such as hemolyzing. The level of damage to the blood depends on a number of factors, one of the main factors being the high shear or shear forces acting on the red blood cells and platelets, which occur in the areas between the pumping elements that are moving relative to each other and relatively close to each other or, more seriously, in contact with each other.

According to National Institute of Health (NIH) publication No. 85-2185 entitled "guidelines for intrinsic action of blood materials," the number of red blood cells and platelets damaged by shear stress depends on the intensity or magnitude of the stress and the time that a defined amount of red blood cells and/or platelets are exposed to the stress in a hematocrit meter. The hematocrit measures the volume percentage of red blood cells in the blood. The results of the blood breakdown test shown in fig. 3 are illustrated using a curve corresponding to the resistance of blood to shear, where shear stress is represented by the Y-axis and exposure time is represented by the X-axis. The area on the curve corresponds to significant particle damage. It was shown that the shear stress that red blood cells can withstand is less than 1000dynes/cm 2. In rotary blood pumps there are many areas, for example, in the hydrodynamic bearing housing and the gaps or gaps between the periphery of the pump blades and the inner surface of the stationary housing, chamber or stator, where the shear forces and stresses generated by the relative motion between the rotor and housing surfaces are greater than the stress values that can be tolerated.

Hydrodynamic bearings exhibit good performance in supporting relatively moving mechanical elements because of the increased fluid pressure within the bearing chamber. This action requires an important annular flow to ensure zero pump operation and high shear stresses due to the relative velocities of the pump elements. Since the high pressure side of the vane and the low pressure side of the vane are connected together at the periphery, a high pressure drop is created in the gap between the periphery of the vane and the inner surface of the housing. Furthermore, as in hydrodynamic bearings, the shear stress is also high due to the gradient of the flow rate in this region.

Blood is a tissue consisting of plasma and several aerosols with different densities. Plasma is the liquid portion of blood and is composed of approximately 90% water. Although plasma is not affected or hardly affected to the above-mentioned shearing force, particles such as red blood cells may be damaged by such shearing force or stress.

Although various efforts have been made to solve or at least reduce the above-mentioned problems of rotary pumps, particularly rotary blood pumps, there remains a need for rotary blood pumps with the ability to reduce or eliminate the harmful shear forces and stresses particularly in the gaps between the rotor and stator or housing, which are important causes of damage to the integrity of the blood.

The following patents describe efforts to address the above-mentioned deficiencies associated with rotary pumps, and in particular with rotary blood pumps.

US patent US4,908,012 to John c. moise discloses an implantable ventricular assist pump having a tubular body within which the rotor and stator of the pump are coaxially mounted, with a purging fluid being introduced into the stator vanes of the pump to avoid discontinuities in the wall of the blood conduit. The purpose of the cited patent is to reduce the size of the implant and minimize the risk of infection by reducing shock, minimizing the tubing through the skin, and directing most of the heat generated by the pump into the blood. The patent neither mentions the problem of shear stress to be found nor addresses the problem. Nor does it mention the kinetic energy of the fluid and indeed the tangential component of the flow velocity is not reduced in terms of the arrangement of the stator vanes.

US patent US5,209,650 to Guy b. As clearly disclosed in this specification, the problem addressed by this invention is leakage of the mechanical seal and wear of the bearing. Shear and shear stress problems are not mentioned. While Lemieux specifically addresses the inclined stationary vanes that cause the liquid from the second stage unitary rotor-impeller assembly to slowly mix, it does not take into account the kinetic and tangential components of the blood flow and in any event, the separation of the axial rotor and the axial stator as disclosed and described by this patent does not overcome this problem.

US patent 5,678,306 to Richard j. bozeman discloses a method of reducing blood damage by optimizing certain blood pump configuration parameters and variations in existing pumping elements. The method includes selecting some of the pump's constituent elements that must have an effect on blood damage, such as the clearance between the vanes and the housing, the number of impeller vanes, rounded or flat vane edges, changes in vane entry angles, the length of the impeller, and the like. The structure variables of each of these elements are selected and the variables are listed in a matrix for comparison of results. Each variable is tested and the total amount of damage to the blood caused by the blood pump is determined, and finally the least hemolytic variable of the constituent elements of each pump is selected as the optimal element. Although considerations are made regarding blood damage and the gap between the shell and the leaflets, no attempt has been made to solve this problem by changing the size of the gap and the leaflet-shell geometry without providing any means to seal the gap at the outer perimeter of the leaflets.

U.S. patent No. 5,055,005 to Kletschka discloses a fluid pump with an electromagnetically driven rotating impeller that is gently lifted by local opposing fluid forces, the impeller being gently floated eliminating the need for bearings and seals in the drive machine. The shear stress generated at the light floating region, which causes blood to be destroyed, is rather high. But no consideration has been made regarding the means for preventing blood from being destroyed under such conditions.

US patent US4,382,199 to issacs discloses a hydrodynamic bearing for a motor for driving a pump of an artificial heart. The stator of the motor has a hole in which the rotor with the impeller can slide and rotate. Both the rotor and impeller are hydrodynamically supported in such a way that the fluid has a tendency to completely suspend the entire rotor/impeller assembly. It is quite clear that there will be high shear stresses between the rotor assembly and the motor stator without providing effective means to solve this problem.

US patent US5,049,134 to Golding et al discloses a blood pump with two hydrodynamic bearings at the end of a rotating impeller. The support involves a screw conveyor that pushes blood through the pump for lubrication and cooling purposes. In addition, the rotatable impeller includes an aperture that allows blood to flow continuously from the blades to the hydrodynamic bearing. The shear stress in the hydrodynamic bearing is high enough to be able to break the blood, and the patent does not provide any solution to this problem.

Other references, such as Dean US3,083,893, Richter US3,276,382, Snyder US2,470,794, and Fuller US1,071,042, provide two or more rotor pumps, but they do not address the problem of how to handle blood and how to seal the gap between the rotor and the housing.

Thus, the number of components of the rotary pump, and in particular the rotary blood pump, is minimized and it is possible to provide a continuous flow of fluid with minimal or no stress, and in particular with minimal or no shear stress or shear forces that could damage the circulating fluid, and in particular the blood within the rotary blood pump, and affect the integrity of the fluid.

Summary of The Invention

It is therefore an object of the present invention to provide a rotary pump for propelling a fluid, in particular a fluid that is protected against any damage, in particular blood, wherein the rotary pump comprises at least one rotor, a housing and means for forming a seal and/or a support at a gap or clearance between the rotor and the housing.

It is another object of the present invention to provide a blood pump with a sealing device, which includes providing a portion of bypass blood to the gap between the rotor and the housing, the portion of blood being composed primarily of plasma free of red blood cells, thereby preventing damage to solid particles and red blood cells.

Another object of the invention is to provide a rotary blood pump comprising at least one rotor, a housing and means for bypassing a portion of the blood under pumping action to the gap between the rotor and the housing for the purpose of forming a seal and/or support, this portion of blood being treated at the pumping site mainly consisting of plasma and other particles, in particular free of erythrocytes, as a result of the centrifugal force generated by the mass of the blood as a result of the rotation of the rotor. Thus, for sealing and/or support purposes, this portion of the bypass blood is free of red blood cells that would otherwise be affected by the shear forces generated at the gap between the rotor and the housing.

It is also an object of the present invention to provide a hydrodynamic seal for a rotary pump of the type comprising at least one rotor mounted in a stator housing, the rotor comprising a hub and at least one fluid propelling vane located in the hub, a gap being defined between the periphery of the rotor and the housing, the seal comprising at least one duct located within the rotor which directs a portion of a bypass fluid under pumping action, the outlet of the duct being located at the periphery of the rotor and the inlet thereof being radially inward relative to the outlet, wherein a portion of the bypass fluid enters from the inlet of the duct and exits from the outlet of the duct and enters the gap, thereby forming a high pressure fluid seal between the rotor and the housing.

Another object of the invention is to provide a rotary pump for driving fluids, in particular blood, comprising a stationary casing, at least one rotor rotating inside the casing, the rotor comprising a hub and at least one impeller blade inside the hub for propelling the fluid, a gap between the periphery of the rotor and the stationary casing, and at least one duct inside the rotor for guiding a portion of the bypass fluid under pumping action, the outlet of the duct being the periphery of the rotor, the inlet of the duct being radially inward with respect to the outlet, wherein the portion of the bypass fluid enters from the inlet of the duct and exits from the outlet of the duct and enters into the gap, thereby forming a high-pressure fluid seal between the rotor and the casing.

A blood pump, comprising: at least one rotor rotatable within a housing, said pump comprising, means between a blood inlet of said pump and said at least one rotor for separating red blood cells from plasma thereby forming a stream of blood comprising predominantly red blood cell-free plasma and another stream of blood having a red blood cell to plasma ratio significantly higher than the previous stream, and means for supplying the stream of blood consisting of red blood cell-free plasma to a gap between said at least one rotor and said housing

It is another object of the present invention to provide a continuous axial flow pump for propelling a fluid in a continuous flow regime without adverse effects thereby minimizing or eliminating damage to the fluid, the axial flow pump having at least one stage including a housing and a rotor arrangement mounted in the housing, the rotor arrangement including at least two adjacent rotors counter-rotating with respect to each other. And hydrodynamic sealing means between the outer periphery of the rotor and the housing, wherein the hydrodynamic sealing means comprises means for separating red blood cells from plasma thereby forming a first stream of blood and a second stream of blood, the first stream of blood comprising primarily red blood cell-free plasma and the second stream of blood having a ratio of red blood cells to plasma substantially higher than the ratio of the red blood cells to plasma of the previous stream; and means for introducing the second stream of blood into the outer periphery of each rotor and into the housing

The above and other objects, features and advantages of the present invention will be more fully understood from the accompanying drawings and description.

Brief description of the drawings

The invention is illustrated by way of example in the accompanying drawings, in which:

FIG. 1 is a partial cross-sectional view of a first embodiment of a blood pump of the present invention;

FIG. 2 is an overall cross-sectional view of the blood pump shown in FIG. 1;

FIG. 3 is an X-Y graph showing the resistance of platelets and red blood cells to shear stress and the time of exposure;

FIG. 4 is a cross-sectional view taken along section line IV-IV in FIG. 2;

FIG. 5 is a graph showing the variation of centrifugal force in a hydrodynamic bearing as a function of the radius of the rotor;

FIG. 6 is a cross-sectional view taken along section line VI-VI in FIG. 2;

FIG. 7 is a cross-sectional view taken along section line VII-VII in FIG. 2;

FIG. 8 is a partial cross-sectional view of a second embodiment of the blood pump of the present invention;

fig. 9 is an overall cross-sectional view of the blood pump shown in fig. 8.

Description of The Preferred Embodiment

Referring now to the drawings in detail, it can be seen from fig. 1 and 2 that the preferred embodiment of the present invention is a rotary pump, and in particular a rotary blood pump, generally designated by the reference numeral P.

Assuming first that the direction of flow and the orientation are from left to right as indicated by the arrow F, the pump preferably comprises an upstream rotor 1 and an adjacent downstream rotor 2, the two counter-rotating rotors being located within a housing stator or casing 3 having a recess 4. The rotor 1 includes: a hub 5 with propulsion blades 6, the blades 6 being at least one blade or preferably four helical blades. The rotor 1 comprises an axial concentric ring 7, the inner surface of which is connected to the periphery of the blades 6, while its outer circumferential surface 8 faces the inner surface of the housing and is slightly separated from the latter so as to form a hydrodynamic gap or slit 9. The permanent magnet 10 is contained within the band 7 so as to cause the rotor 1 to rotate within the housing under the magnetic action of a stator coil 12 wound coaxially about the axis 1, the stator coil 12 surrounding the band 7 or the axisymmetrical band and the magnet 10. Although the pump of the present invention is preferably provided with two

adjacent rotors

1 and 2, the present invention can be easily applied to a pump with one rotor such as the rotor 1.

Assuming that the pump has only one rotor, rotor 1, blood is drawn in from the left side of the figure and guided along the housing to the right side of the figure under the propulsion of the blades. Due to the relative movement between the band defining the circumference of the rotor and the housing, high shear or shear stresses will occur in the gap or slit 9, more precisely between the outer circumferential surface 8 of the band and the inner surface of the housing 3. Under such shear forces, the particles in the blood can be severely damaged, but the blood must enter the gap to give hydrodynamic support to the rotor. In other words, the blood within the housing completely suspends the rotor, but the blood is subject to destructive shear forces in the suspended region, i.e., in the pump clearances.

In accordance with the present invention, blood can be used to achieve this desired support without subjecting the integrity of the blood to such damaging stresses. More specifically, a portion of blood, which is comprised of plasma, is separated from the blood stream and bypassed into the gap or crevice for support and sealing. This portion of the bypass blood is not affected by shear forces as long as the content of particles, such as red blood cells, is low. The red blood cells have a better sensitivity to pressure and shear forces like those present in the gap between the rotor and the housing.

According to the invention, means are provided for introducing the portion of the bypass fluid into the gap, which means comprise at least one duct 13 in the rotor, the outlet 14 of which is located at the periphery of the rotor and the inlet 15 of which is located radially inwards with respect to the outlet, wherein the portion of the bypass fluid enters from the inlet 15 and exits from the outlet 14 into the gap 9, thereby forming a high-pressure liquid seal between the rotor and the housing. More particularly, the duct comprises: a first portion or first conduit 16, the first conduit 16 extending radially from the inlet 15 towards the centre of the rotor so as to direct said bypass fluid portion into the centre of the rotor; a second section or second duct 17, the second duct 17 communicating with the first duct, the second duct extending radially from the centre of the rotor towards the outlet 14, so as to direct the portion of fluid from the centre of the rotor towards the outlet and into the gap.

The conduit 13 behaves like a centrifugal pump, since the inlet 15 is located radially inwards in the rotor with respect to the location of the outlet 14. The first conduit 16 will suck blood close to the circumferential surface of the hub 5 and direct this part of the bypassed blood to the radially outward outlet 14 at the peripheral surface of the band 7. The hub 5, the blades 6 and the band 7 are preferably one integral piece, and the second duct 17 passes through the hub, the blades and the band. Under the pumping action, the blood, and more particularly in the region of the rotor, is subjected to a rotational movement which causes the heavier particles in the blood to be pushed radially outward toward the periphery of the pump, that is, toward the housing. As a result of this effect, the red blood cells are separated radially outward from the peripheral surface 18 of the hub, while the plasma is close to the surface 18 of the hub. Since the inlet 15 is located on the surface 18 of the hub 15, most of the blood entering the inlet will be composed of plasma that is free of red blood cells or very low in red blood cells.

In addition to the aforementioned effects, the device of the present invention is capable of separating suspended particles of blood, such as red blood cells, which may be damaged by shear stress. At the inlet region of the duct 16, these particles are separated from the plasma, since the side walls of the duct are subjected to a rotational movement. Under the effect of this motion, the blood particles are forced to follow a curved path that has the opposite natural tendency to follow a straight line segment at a constant velocity. This imparts to the particles an inertial force due to the rotational movement, i.e. a centrifugal force which prevents particles heavier than plasma from entering the conduit. The pipe 17 in its impeller region operates like a centrifugal pump with the pressure increasing as the radius of the pipe increases closer to the pipe outlet at the gap.

The sealing and/or bearing effect in the high-shear region, i.e. in the gap between the blade and the housing, can be achieved by introducing a bypass portion of blood with a low particle content into the gap. This seal is effective in separating particles in the blood and directing the fluid into the region of the pump having higher shear stress. For a given conduit diameter and a given rotor rotational speed, the amount of plasma with a lower particulate content introduced into the region of the pump with higher shear stress can be defined and controlled.

In a preferred embodiment with two

rotors

1 and 2, the invention works in a similar manner as will be described below. The rotor 2 comprises a hub 19 with propulsion blades 20, which are at least one blade or preferably four helical blades. The rotor 2 comprises an outer coaxial concentric band 21, otherwise known as an axisymmetric band, the inner surface of which is connected to the periphery of the blades 20 and the outer peripheral surface of which faces the inner surface of the housing and is slightly spaced therefrom so as to form a hydrodynamic gap or gap 23. The belt loop 21 comprises permanent magnets 24 to cause the rotor 2 to rotate about the axis 11 within the housing under the magnetic influence of a stator coil 25 wound about the axis 11 and surrounding the belt loop 21 and the magnets 24.

As mentioned above, high shear or shear stresses are generated between the outer periphery of the rotor within the gap or gap 23 defined by the outer peripheral surface of the band 21. To counteract this effect, sealing means are provided as in the rotor 1. Such means comprise at least one duct 26 located within the rotor, the outlet 27 of which is located at the outer periphery of the rotor and the inlet 28 of which is located radially inwards with respect to the outlet, wherein the bypass fluid portion enters from the inlet 28 at the outer peripheral surface 31 of the hub 19 and exits from the outlet 27 and enters the gap 23. More specifically, the duct comprises a first portion or duct 29, the first duct 29 extending radially from the inlet 28 towards the centre of the rotor; a second section or conduit 30, the second conduit 30 communicating with the first conduit, the second conduit extending radially from the centre of the rotor to the outlet 27.

Fig. 4 shows a cross-sectional view of the first section 29 of the tube 26 along the cross-sectional line IV-IV in fig. 2. As shown in fig. 4, the first portion 29 is actually a cylindrical passage formed between the inner walls of the hub 19. The central portion 34 maintains the integrity of the hub part, the hub being separated by the passage 29, and the apertures 26 being provided in the portion 34 to maintain the passages 29 and 30 in fluid communication. Although for the sake of clarity the section line IV-IV is made along the ducts 29 of the rotor 2, the ducts 16 of the rotor 1 are of the same construction, the passages of the ducts 16 are also cylindrical and have a medium-sized bearing portion with small holes.

Fig. 6 shows a cross-sectional view of the second portion 17 of the pipe 13 along the cross-sectional line VI-VI in fig. 2. The structure of the ducts 30 of the rotor 2 is the same, although for the sake of clarity the section line VI-VI is made along the ducts 17 of the rotor 1.

Fig. 7 shows a cross-sectional view of the rotor 1 along the cross-sectional line VII-VII in fig. 2. Although for the sake of clarity it is along the section line VII-VII of the rotor 1, the structure of the rotor 2 is the same.

Although both

ducts

13 and 26 of the

rotors

1 and 2 with the first and

second ducts

16, 17, 29, 30 have been illustrated at the downstream ends of the

rotors

1, 2, such ducts may be provided at any other location of the rotors, as long as the inlet is located radially inward with respect to the outlet of the duct.

In the following, the centrifugal effect of the rotational movement acting on the blood and the part of the blood bypassing the

conduit

13, 26 will be explained. When explained only one of the rotors is involved, but the same concept applies to the other rotor. As the rotor rotates, the side wall 33 also rotates at an angular velocity ω, the pressure in the pipe at the center of the rotor being lower than the pressure at the inlet of the pipe. Due to this pressure drop, blood enters from the

inlets

15, 28, where the blood particles are influenced by the centrifugal force, which is determined by the following equation:

f_centr＝mω²r

wherein:

F_centr: centrifugal force

m: mass of fine particles

ω: angular velocity

r: distance of particles from rotor longitudinal axis

Particles with a mass greater than that of plasma are subjected to a greater centrifugal force. Figure 5 shows that the centrifugal force has the greatest value at the

duct inlets

15, 28, where the particle separation is greatest. Thus, the bypass blood portion has a minimal particulate content when it reaches the hub center. This portion of blood flows through the conduit portions 17, 30 outwardly from the center of the hub with an energy magnitude that can be mathematically expressed by bernoulli's equation in terms of a coordinate system referenced to the rotor rotation:

\frac{w_{1}^{2}}{2 g} + \frac{p_{1}}{γ} - \frac{{(r_{1} ω)}^{2}}{2 g} = \frac{w_{2}^{2}}{2 g} + \frac{p_{2}}{γ} - \frac{{(r_{2} ω)}^{2}}{2 g} + Δh - - - (1)

wherein:

w: relative velocity in a pipe

p: pressure of

ω: angular velocity of rotor

g: acceleration of gravity

γ: weight of unit

Δ h: energy drop of blood between inlet and outlet

Reference numeral 1 denotes an inlet portion

Reference numeral 2 denotes an outlet portion

Rearranging the terms of equation (1) yields the following equation:

\frac{p_{2} - p_{1}}{γ} = \frac{w_{2}^{2} - w_{1}^{2}}{2 g} + \frac{ω^{2} (r_{2}^{2} - r_{1}^{2})}{2 g} - Δh - - - (2)

if the inlet and outlet cross-sections are the same, then the relative velocity of the fluid within the conduit is constant;

w₁＝w₂

the energy drop of the fluid between the inlet and the outlet is proportional to the flow rate circulating through the pipe,

Δh = ξ \frac{Q^{2}}{2 g}

wherein:

q: is the circulation flow rate in the pipeline,

xi: is the damping coefficient of the pipe and is related to the length, diameter and cross-sectional area of the pipe. The coefficients are substituted into equation (2):

\frac{p_{2} - p_{1}}{r} = \frac{ω^{2} (r_{2}^{2} - r_{1}^{2})}{2 g} - ξ \frac{Q^{2}}{2 g} - - - (3)

p₁、p₂and xi is related to the flow conditions in the pump and the pumping rate of the pump. r is₁R of₂The values may be selected during the design of the pump. The flow Q circulating in the pipe is defined by equation (3). The value of Q is essential for hydrodynamically sealing the gap or gap of the support and may also be determined by selecting an appropriate combination from the pipe shape, pipe length, size and diameter according to equation (3).

Although the pump of the present invention has been illustrated and described with a sealing/bearing arrangement and recess 4, the pump of the present invention may comprise only two adjacent impellers or

rotors

1, 2. The blades 6 are coiled in opposite directions with respect to the blades 20. The

rotors

1, 2 rotate in opposite directions about the axis 11 of the pump in accordance with the concepts of the present invention. Depending on these directions of rotation, the left side of the figure 1 corresponds to the inlet F of the pump, while the right side of the figure is the outlet of the flow. Preferably, the outer ends of the

rotors

1, 2 are tapered to accommodate the flow of fluid. The ends of the

rotors

1, 2 facing each other on the inside are adjacent to each other so that when the rotor 1 is the inlet rotor and the rotor 2 is the outlet rotor, the outlet of the rotor 1 is close to the inlet of the rotor 2. The terms "inlet" and "outlet" are used to refer to the rotor on the inlet side of the pump and to the rotor on the outlet side of the pump. Obviously, the inlet and outlet of the pump depend on the direction of rotation of the rotor.

The rotor 1 is mounted in a conventional manner in a housing, preferably a cylindrical or tubular housing, and the

stator motor elements

12, 25 are used to drive the rotor. The first rotor 1 is driven by the stator motor 12 to rotate and transfer energy to the fluid flow, in particular the blood flow, and to increase the tangential component of the velocity of the fluid flow. The rotor 2 rotates under the action of the stator motor element 25 and transfers the pressure energy to the liquid flow and eliminates the above-mentioned tangential component for a given combination of head and discharge or output quantity at the outlet side of the pump. The

blades

6, 20 are wound around the rotor, more precisely the blades extend in a helical manner on the rotor, wherein the helical direction of the blades 6 is defined as a first direction and the helical direction of the blades 20 is defined as a second direction opposite to the first direction.

According to another embodiment of the present invention, fig. 8 and 9 show a rotary pump different from the above-described embodiment, wherein the housing of the second embodiment does not have a recess for accommodating the rotor, but the rotor is mounted in the housing by mounting means.

F denotes the direction and direction of flow and the pump preferably comprises an upstream rotor 35 and an adjacent downstream rotor 36, which counter-rotate within a tubular housing, stator or casing 37. The

rotors

35, 36 may be connected by a main shaft (not shown) to rotate about the same axis in different directions and, if desired, at different speeds. The

rotors

35, 36 each comprise a

hub

39, 40 with at least one

impeller blade

41, 42, each preferably having four helical blades.

The

hubs

39, 40 include permanent magnets 55, 56 for causing the rotor to rotate under the influence of the electromagnetic field induced by the stator coils 43, 44.

The outer periphery of the rotor is defined by the outermost circumferential surfaces or

peripheral edges

45, 46 of the

vanes

41, 42, with a gap or

clearance

47, 48 defined between the

edges

45, 46 and the inner surface of the housing 37. The

rotors

35, 36 are mounted inside the housing by mounting means which are able to hold both rotors on the housing. The mounting device comprises respective conical supports 49, 50 and a common central support 51, which supports 49, 50 and 51 are connected to the housing by

respective guide vanes

52, 53 and 54, which guide

vanes

52, 53 and 54 are circumferentially isolated around the conical supports and the central support. The support means, i.e. the cone support, the central support and the guide vanes, are fixed to the housing by fixing means, such as screwing and welding. The

hubs

39, 40 are rotatably mounted on the

supports

49, 50 and 51 by suitable bearing means, for example by ball bearings, needle bearings or the like, which are schematically indicated and designated by reference numerals 57, 58 and 59.

The sealing and/or support means of the invention are arranged in the rotor in the same way as used in the first embodiment described above, except that no band concentric with the rotor is provided, the blade edges 45, 46 are free from the shroud member and directly face the inner surface of the casing. As in the first embodiment of the invention, the shearing forces in the

slits

47, 48 can be counteracted by feeding a portion of the blood into the slits. More particularly, a portion of the blood, which is comprised of plasma, is separated from the blood stream and bypassed to the gap or slit for sealing purposes. This portion of the bypass blood is minimally affected by shear forces, provided that its red blood cell content is sufficiently low.

According to a second embodiment of the invention, the means for introducing the portion of the bypass blood into the gap comprise at least one

duct

60, 61 respectively located in each

rotor

35, 36. Each

duct

60, 61 has at least one

outlet

62, 63 located at the periphery of the rotor, i.e. at the

peripheral edge

45, 46 of the

blades

41, 42, and at least one

inlet

64, 65, the at least one

outlet

62, 63 being located radially inwards with respect to the outlet, i.e. at the peripheral surface of the

hub

39, 40. This portion of the bypassed blood enters through

inlets

64, 65 and exits through

outlets

62, 63 and flows through gap 47, thereby forming a high pressure liquid seal between the outer peripheral edge of the vane and the housing, respectively. More preferably, each of the pipes includes: a first portion or conduit 66, 67, the first conduit 66, 67 extending radially from the

inlet

64, 65 to a central conduit to direct said bypass fluid portion into the central conduit of the rotor; a second portion or conduit 70, 71, the second conduit 70, 71 being in fluid communication with the central conduit and extending radially from the centre of the rotor to the

outlet

62, 63 to direct the portion of fluid from the centre of the rotor to the outlet and into the

gap

47, 48.

By substantially the same effect as in the first embodiment, blood enters the

inlets

64, 65 and, since these inlets are located radially inwards in the rotor with respect to the

outlets

62, 63, the

ducts

60, 61 act, for example, like centrifugal pumps, so that at the inlets a portion of the blood is sucked in, which has the lowest content of red blood cells, flows through the ducts 66, 67, through the central ducts 68, 69 and is guided into the

gaps

47, 48 by the ducts 70, 71 and the

outlets

62, 63. As in the embodiment shown in fig. 1, the pump may include only one rotor employing the present technique. More particularly, according to the invention, the pump of fig. 8, 9 may comprise a rotor 35 with the sealing means 60, 62 or 64, without the rotor 36, but with the

bearings

49, 51, 52, 54 arranged in the positions shown in the figures.

While the preferred embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.

Claims

1. Hydrodynamic sealing device for a rotary pump, wherein the rotary pump comprises: at least one rotor mounted in a stationary housing, the rotor including a hub, a gap being defined between a periphery of the rotor and the housing, the sealing arrangement including:

at least one conduit located within the rotor and adapted to direct a portion of the bypassed fluid under pumping action, the outlet of the conduit being located at the periphery of the rotor and the inlet of the conduit being radially inward relative to the outlet, wherein the bypassed portion of the fluid enters the inlet of the conduit and exits the outlet of the conduit and enters the gap, thereby forming a high pressure fluid seal between the rotor and the housing.

2. A sealing device as claimed in claim 1, wherein the duct passes at least partially through at least one blade, the outlet of the duct being located at the peripheral edge of the blade and the inlet of the duct being located at or near the peripheral surface of the hub, the gap being located between the peripheral edge of the blade and the housing.

3. The seal of claim 1, wherein the rotor includes a coaxial outer band having an axially axisymmetric outer surface, the blades being secured between the hub and the band, the rotor outer periphery being defined by the outer peripheral surface of the band, the gap being between the outer peripheral surface of the band and the housing.

4. A seal according to claim 3, wherein the housing has an annular recess in which the band is rotatably mounted, the gap being between the band and the housing in the recess.

5. The seal of claim 1, wherein the at least one conduit comprises:

a first conduit portion extending radially from the inlet toward the center of the rotor to direct the bypass flow portion into the center of the rotor,

a second conduit portion in fluid communication with the first conduit portion, the second conduit portion extending radially from the center of the rotor toward the outlet to direct the portion of the fluid from the center of the rotor toward the outlet and into the gap.

6. The seal of claim 5, wherein the rotor includes a coaxial outer band having an axially axisymmetric outer surface, the blades being secured between the hub and the band, the rotor outer periphery being defined by the outer peripheral surface of the band, the gap being between the outer peripheral surface of the band and the housing.

7. The seal arrangement of claim 6, wherein the first duct portion extends in a radial direction from the center of the rotor to the outer peripheral surface of the hub, and the second duct portion extends radially from the center of the rotor and passes through the blades and the band and forms an opening at the outlet in the outer peripheral surface of the band.

8. The seal of claim 7, wherein the housing has an annular recess in which the band is rotatably mounted, the gap being between an outer peripheral surface of the band and the housing.

9. The seal of claim 2 wherein the hub includes a plurality of impeller blades and each blade includes at least one conduit extending radially outwardly through the blade.

10. A rotary pump for driving a fluid, the pump comprising:

a fixed shell body,

at least one rotor rotatably mounted within said housing, said rotor comprising a hub and at least one impeller blade on said hub for propelling a fluid,

a gap between the periphery of the rotor and the stationary casing, an

At least one duct in the rotor, said duct directing a portion of the bypass fluid under pumping action, the outlet of said duct being located at the outer periphery of the rotor, the inlet thereof being located radially inward with respect to the outlet,

wherein the bypass fluid enters from the inlet of the duct and exits from the outlet of the duct and enters the gap, thereby forming a high pressure liquid seal between the rotor and the housing.

11. A pump as claimed in claim 10, wherein the conduit passes at least partially through at least one blade, the outlet of the conduit being located at the peripheral edge of the blade and the inlet of the conduit being located at or near the peripheral surface of the hub, the gap being located between the peripheral edge of the blade and the housing.

12. The pump of claim 10, wherein the rotor includes a coaxial outer band having an axially axisymmetric outer surface, the vanes being secured between the hub and the band, the rotor outer periphery being defined by the outer peripheral surface of the band, the gap being between the outer peripheral surface of the band and the housing.

13. The pump of claim 12 wherein the housing has an annular recess in which the band is rotatably mounted, the gap being between the band and the housing in the recess.

14. The pump of claim 10, wherein the at least one conduit comprises:

15. The pump of claim 14, wherein the rotor includes a coaxial outer band having an axially axisymmetric outer surface, the vanes being secured between the hub and the band, the rotor outer periphery being defined by the outer peripheral surface of the band, the gap being between the outer peripheral surface of the band and the housing.

16. The pump of claim 15, wherein the first conduit portion extends in a radial direction from the center of the rotor to the outer peripheral surface of the hub, and the second conduit portion extends radially from the center of the rotor and passes through the blades and the band and forms an opening at an outlet in the outer peripheral surface of the band.

17. The pump of claim 16 wherein the housing has an annular recess in which the band is rotatably mounted, the gap being between the band and the housing in the recess.

18. A pump as claimed in claim 11, wherein the hub comprises a plurality of impeller blades and each blade comprises at least one conduit passing radially outwardly through the blade.

19. The pump of claim 10, wherein said at least one rotor comprises:

two adjacent rotors independent of each other and having opposite directions of rotation.

20. The pump of claim 19 wherein said impeller blades extend helically on the outer peripheral surface of the hub and the helix angle of said helical blades on one rotor is in the opposite direction to the helix direction of said helical blades on the adjacent rotor.

21. A pump as in claim 19 wherein said rotors include an upstream rotor having an upstream end and a downstream rotor having an upstream end and a downstream end, said downstream end of said upstream rotor facing said upstream end of said adjacent downstream rotor, said conduits being distributed at the downstream ends of said rotors.

22. A blood pump, comprising: at least one rotor rotatable within a housing, said pump comprising means for providing a portion of bypass blood to a gap, said means comprising at least one conduit within the rotor, said conduit having at least one outlet at the periphery of said rotor and at least one inlet disposed radially inwardly relative to said outlet, wherein a portion of said bypass fluid enters from said inlet of said conduit and exits from said at least one outlet of said conduit and enters said gap, thereby forming a high pressure fluid seal between said rotor and said housing.

23. A continuous axial flow blood pump having at least one stage, said pump comprising a housing and at least two adjacent rotors mounted in said housing for rotation in opposite directions, and hydrodynamic sealing means between the outer periphery of said rotors and said housing, wherein said sealing means comprises at least one conduit in said rotors which, under pumping action, directs a portion of a bypass fluid, said conduit having at least one outlet at the periphery of said rotors and at least one inlet disposed radially inwardly of said outlet, wherein a portion of said bypass fluid enters said inlet of said conduit and exits said at least one outlet of said conduit and enters said gap, thereby forming a high pressure fluid seal between said rotors and said housing.